/*
 * Copyright 2011 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.droid.mvvmlib.base;

/**
 * Precondition checkers modeled after {com.google.common.base.Preconditions}. Duplicated here
 * to avoid the dependency on guava in Java client code.
 */
public class Preconditions {

    /**
     * Throws {@link NullPointerException} if the {@code reference} argument is
     * {@code null}. Otherwise, returns {@code reference}.
     */
    public static <T> T checkNotNull(T reference) {
        if (reference == null) {
            throw new NullPointerException();
        } else {
            return reference;
        }
    }

    /**
     * Throws {@link NullPointerException} if the {@code reference} argument is
     * {@code null}. Otherwise, returns {@code reference}.
     */
    public static <T> T checkNotNull(T reference, Object errorMessage) {
        if (reference == null) {
            throw new NullPointerException(String.valueOf(errorMessage));
        } else {
            return reference;
        }
    }

    /** Throws {@link IllegalStateException} if the given {@code expression} is {@code false}. */
    public static void checkState(boolean expression) {
        if (!expression) {
            throw new IllegalStateException();
        }
    }

    /** Throws {@link IllegalStateException} if the given {@code expression} is {@code false}. */
    public static void checkState(boolean expression, Object errorMessage) {
        if (!expression) {
            throw new IllegalStateException(String.valueOf(errorMessage));
        }
    }

    /** Throws {@link IllegalArgumentException} if the given {@code expression} is {@code false}. */
    public static void checkArgument(boolean expression) {
        if (!expression) {
            throw new IllegalArgumentException();
        }
    }

    /** Throws {@link IllegalArgumentException} if the given {@code expression} is {@code false}. */
    public static void checkArgument(boolean expression, Object errorMessage) {
        if (!expression) {
            throw new IllegalArgumentException(String.valueOf(errorMessage));
        }
    }

    // Do not instantiate.
    private Preconditions() {
    }
}
